Sensorless control is one of the most important topics in the field of motor drives, for which we assume only access to electrical coordinates, i.e., the stator currents and voltages. It is of paramount importance in industry since sensorless control of motors can reduce hardware complexity, improve reliability, and achieve cost reduction [1]}, [2]}. Meanwhile, this problem has received particular attention from the automatic control community due to its theoretical interests, i.e., the dynamical model of the permanent magnet synchronous motor (PMSM) does not belong to any observable canonical forms that have been studied comprehensively [3]}. To be precise, the main constructive challenges arise from the highly nonlinear output functions.
